A large variety of hydraulic components are available and are selected depending on the end use of the article under construction. Outdoor statuary, architectural moldings, mortars, grouts, tiles and the like are often made of concrete because it withstands water and weather. Gypsum is generally reserved for indoor use, such as plaster or drywall. Both of these materials form a settable slurry when added to water that can be used in a variety of ways. The slurry can be applied with a trowel for patching. It can be molded to form statuary. Either material can be used in mortars and grouts to set tiles or bricks in place.
However, concrete and gypsum both harden to be very rigid, brittle materials. Once set, it is not practical to change their shape. For example, when used as a grout for ceramic tile, if there is a shift in the underlayment, the grout usually cracks because it cannot deform to move with the shift. When subjected to a sudden impact, concrete and gypsum often break because they cannot absorb the force by deformation.
Another disadvantage of concrete is the length of the time needed to cure the material. Concrete cannot hold its own weight for hours, and does not fully cure for a week or more. When making molded articles, the molds cannot be turned around and reused until the following day. If the concrete is used to make something that must bear the weight of other articles, such as the basement floor in a new house, the floor cannot be used for several days until the concrete is more fully cured.
Gypsum has a considerably shorter setting time, but has its own disadvantage in the amount of dust generated when, for example, joint compound is finished. To smooth the surface of a joint and feather the edges so that they blend with the adjoining dry wall, joints are sanded, creating quantities of very fine dust that can be carried great distances before settling out. In addition to leaving dust some distance from the site being patched, this fine dust becomes a nuisance to those who breathe it.
U.S. Pat. No. 6,455,615 to Yu discloses a flexible polymer modified cement that can be used alone or on a substrate. It is disclosed for use in concealed areas of construction engineering, water conservancy projects and municipal works. A hydraulic cement, a polymer dispersion and water are calendared to form sheets, then dried until the composition is firm. The hydraulic component optionally includes from 20% to about 50% other hydraulic components, including fly ash, silica fume, metakaolin and slag.